Present invention relates to an arrangement for warming of oil in a gearbox.
When an engine-powered vehicle is started after a period of being switched off, the oil in a gearbox is at substantially the same temperature as the surroundings. When the surroundings are at a low temperature, the oil in the gearbox is in a more or less viscous state. During cold starts of the vehicle, the viscous consistency of the oil therefore results in the consumption of a large amount of extra energy for driving the components of the gearbox. The viscous consistency of the oil also means that greater force is required for engaging different gears in the gearbox. The oil in the gearbox is mainly warmed by the friction heat generated by the components of the gearbox performing their mechanical work. Such warming is not particularly effective, so a relatively long time may be required for the oil in the gearbox to reach its operating temperature after a cold start. After a cold start of the vehicle, the components of the gearbox have therefore to be provided with extra driving power for a relatively long time until the oil in the gearbox reaches a desired temperature and consistency. Partly for this reason, a large amount of extra fuel is consumed during a cold start.
DE 44 31 351 refers to an arrangement for warming a combustion engine and the oil in a gearbox during cold starts of a vehicle. The arrangement comprises a pipe system with a circulating medium. A heat source supplies heat to the circulating medium before the latter is circulated through the combustion engine and/or through a heat exchanger which warms the oil of the gearbox. The circulating medium may take the form of the coolant of the existing cooling system which cools the combustion engine. The heat source operable to warming the circulating medium is not herein specified in more detail. The only point to note is that the heat source does with advantage use latent heat energy for warming the circulating medium.